Rebar Anchorage orientation

[Enhineyero]

Hi, does anyone know why the details for anchorage hook of rebars (beam rebars hooking at columns) are facing towards each other. that is the bottom rebar hook anchorage is going up, while the top bar rebar hook anchorage is going down.

Does the orientation of the rebar hook have anything to do with the degree of fixity of the beam?

I have always thought that they were detailed that way due to practicality on site only. because it is not possible (unless you drill a hole) to hook the beam bottom bars going down if column below it is already casted. While hooking the beam top bar oriented upwards will make the rebar protrude when at the beam is at the upper most level (because there is no more column above the beam).

Any thoughts?

 

[JAE]

You ask the question and I believe you answered it. It is essentially practicality of the concrete placing sequence.

Columns are typically constructed up to the bottom of the beams with their vertical bars extended beyond. The beam rebar cages are then dropped into the formwork and therefore any bottom bars with hooks cannot hook downward into the as-cast column.

 

[TXStructural]

JAE is correct, but it there is also regional variation. I would add that how the engineer details these bars determines what is built. If you need a particular continuity, show it in your details. Constructibility is a primary concern in the industry, so be sure that what you issue can be built using standard means and methods.

I should refer you to the CRSI Placing Reinforcing Bars book for a better understanding of construction issues.

 

[WillisV]

The orientation of the bars does affect the confinement of the panel zone. For high moments it is recommended to hook bars towards each other. This is true even say at the base of a pedestal into a footing that has high moments, where one might typically see the hooks rotated outwards into the footing, it is better structurally to rotate them inwards to confine the joint. See p14-15 of: www.conveyinc.com/things/crsidesigner.pdf